In recent years, there has been an abrupt demand for a decrease in size and weight of a variety of electronic devices, and thus there is a demand for a decrease in size or thickness of a condenser, an inductor, or the like which is embedded in an IPD chip having a plurality of passive elements formed on a substrate. For a decrease in the thickness of an inductor, compared to a wirewound inductor of the related art having a structure in which a wire is wound in a bulk magnetic material, for example, a thin film inductor or the like having a structure in which a spiral planar coil is inserted in a magnetic material such as a ferrite is proposed.
Since a magnetic material used in an inductor generally shows a high magnetic permeability in a high frequency range, a ferrite thin film or the like formed by using a ferrite-based material has been thus far used widely. Thus far, as a method of manufacturing a ferrite thin film, researches and developments have been made mainly for a forming method in which a vacuum process such as a sputtering method or chemical vapor deposition is required; however, in this method, it was necessary to introduce an expensive apparatus to the process, and thus there was a problem with costs such as an increase in initial investment. Meanwhile, while a forming method or the like by using a spin spraying method to which non-electrolytic plating is applied has been also studied; however, in the spin spraying method, while there is a merit that a ferrite film can be formed by using a relatively cheap apparatus, since a liquid including a large amount of a raw material is used during forming of a film, there was a problem in terms of the environment.
Therefore, a sol-gel method is attracting attention as a method of forming a ferrite thin film, which is not a spin spraying method and replaces a sputtering method or the like. In the sol-gel method, a vacuum process, which is used in the sputtering method or the like, is not required, and a ferrite thin film can be formed by using relatively simple and low-cost processes of preparation, coating, drying, and firing of a composition material. As a method of forming a ferrite thin film by using the sol-gel method, in the past, a method of forming a NiCuZn ferrite thin film by coating a mixed solution including iron nitrate, nickel nitrate, N,N-dimethylformamide, zinc acetate, and copper nitrate on a Si substrate on which SiO2 is formed by using a spin coating method, drying the Si substrate on which the mixed solution is coated at 120° C. for 10 minutes so as to remove the solvent, and heating the resultant at 400° C. for 30 minutes so as to be thermal decomposed was disclosed (for example, refer to Non Patent Document 1).